Add automation for test-plan sub-issues on Epic and Story issues

[yusufttur]

Technical TODO

Summary

Add an automation that creates and maintains a test-plan issue as a sub-issue when a dedicated trigger label is added to a parent issue.

Supported parent issue types:

• Epic
• Story

Scope

• Triggered by a dedicated label on the parent issue
• Test-plan issue is created in the same repository as the parent issue
• Only one test-plan issue may exist per parent issue
• Child issue has no dedicated label
• Child issue identity is tracked via a hidden body marker

Marker

Each generated test-plan issue should contain this hidden marker in its body:

<!-- test-plan-for: owner/repo#1234 -->

Example:

<!-- test-plan-for: shopware/SwagCommercial#456 -->

Expected Behavior

Label added

When the trigger label is added to an issue of type Epic or Story:

1. Look up an existing test-plan issue in the same repository using the marker.
2. If no matching issue exists:

• create a new test-plan issue
• add the marker to the issue body
• link it as a sub-issue of the parent

3. If a matching issue already exists:

• reuse it
• reopen it if it is closed
• ensure it is linked as a sub-issue

4. If multiple matching issues exist:

• do not create another issue
• report the conflict for manual cleanup

Label removed

When the trigger label is removed from the parent issue:

1. Look up the existing test-plan issue by marker.

• If found:
• close it
• do not delete it
• keep the sub-issue link intact

2. If not found:

• do nothing

Relabel

When the trigger label is added again later:

1. Look up the existing test-plan issue by marker.
2. If found:

• reopen it if closed
• reuse it
• ensure it is linked as a sub-issue

3. If not found:

• create a new one

Non-goals

• Delete test-plan issues automatically
• Add a dedicated label to the child issue
• Synchronize child title/body after creation
• Support parent issue types other than Epic and Story
• Add scheduled reconciliation in the first iteration

Edge cases

• Label added multiple times
• Label removed and added again
• Existing child issue already present
• Existing child issue closed
• Existing child issue manually unlinked
• Existing child issue manually deleted
• Duplicate child issues found for the same parent
• Label added to unsupported issue type

Acceptance criteria

• Adding the trigger label to an Epic or Story creates exactly one test-plan sub-issue if none exists
• Adding the trigger label again does not create duplicates
• Removing the trigger label closes the existing test-plan issue
• Removing the trigger label does not delete the test-plan issue
• Re-adding the trigger label reopens and reuses the existing test-plan issue
• The child remains linked as a sub-issue after unlabeling
• Multiple matching children are detected and reported instead of creating more
• Unsupported parent issue types do not create a test-plan issue